The present invention concerns the field of textile industry, particularly the treatment of threads by means of thermal treatment machines that are commonly called heat setting machines, and its object is such a machine comprising a device for positioning the conveyor belt during its advance, which is equipped with means to hold the latter at a height separation with respect to the position control means.
The thermal treatment machines consist essentially of a pressurized enclosure for the thermal treatment of textile threads that are deposited on a conveyor belt, passing through said enclosure, which is closed at its two ends by sealing heads comprising each a frame or moving body holder fixed to the pressurized enclosure, a pair of superposed horizontal rollers, which are pressed against the opposite faces of the conveyor belt, and sealing means to form a sealing closure between the rollers and the frame.
The horizontal rollers are actuated by tightening means that allow the movement of at least one of the rollers in the direction of the other, to tighten them against the conveyor belt. In addition, the sealing heads are mounted, each through the intermediary of its frame or moving body holder, in a pivoting way with respect to a vertical median axis, and they are connected to the treatment enclosure through the intermediary of a bellows that extends between the vertical pivoting axis and the frame or moving body holder of said sealing heads.
During operation, the conveyor belt may undergo drift between the inlet and the outlet of the thermal treatment machine, which drift may result in jamming in the interior of the machine, if a predetermined limit is exceeded, and result at least in stoppages of the machine to correct the problem, and possibly in damage.
It has been proposed to solve this problem by providing a means for positioning the conveyor belt between the inlet and outlet heads, through the intermediary of cells for the detection of the position of said belt at the ends of the machine, i.e., close to the sealing heads, where these detection cells deliver a control signal for the modification of the position of the heads by means of actuators that act on the frame or moving body holder of the latter causing them to pivot. Such a pivoting of the sealing heads has the effect of modifying the position of the axis of the sealing rollers, so that the conveyor belt is adjusted in the opposite direction of the observed deviation, as a result of the clamping of the conveyor belt between the superposed horizontal rollers. Indeed, while the sealing head pivots, the conveyor belt is driven in a pivoting motion, because it is clamped between the longitudinal rollers, along a transverse generatrix, which induces a corresponding correction of the belt to correct its drift and return it to its normal operating position.
In general, the means for the detection and correction of the position of the conveyor belt of such machines are perfectly suited to ensure a correct positioning of said conveyor belt. However, a detection problem arises, and thus a problem in the correction of the deviation, if the conveyor belt is bent due to aging. Indeed, the sensors that detect the position of the conveyor belt at the inlet and at the outlet of the machine are sensitive to the deformation of this conveyor belt.
Moreover, because frames or moving body holders of the sealing heads are installed, each on a vertical pivoting axle provided at a distance from said frames or moving body holders of the sealing heads, it is necessary to take into account by anticipation the pivoting of said sealing heads, which is increased by a lever arm effect due to the distance between the pivoting axis and the plane of the superposed horizontal rollers, and due to the distance between the sensors and the heads, resulting in an amplification of the correction of the observed drift.
In addition, the installation of the sealing heads, in the manner described above, results in a considerable overhang of the heads, and thus corresponding stresses on the pivoting axis, requiring a corresponding dimensioning of all the mounting elements of said heads.
From FR-A-2 894 258, a device for positioning the conveyor belt is also known, for machines for the thermal treatment of threads that consist of a pressurized enclosure, through which a conveyor belt passes, and which is closed at each end by a sealing head mounted on a frame or moving body holder that is connected to the pressurized enclosure through the intermediary of a bellows, where each sealing head comprises a pair of superposed horizontal rollers which are pressed against the opposite faces of the conveyor belt. This device comprises a positioning means and a position control means acting on a very short area in the immediate proximity of each sealing head.
To this effect, the positioning means consists of a pivoting axle of the frame or moving body holder that is integrally connected directly to said frame or moving body holder, and of an actuator of the pivoting of the frame or moving body holder through the intermediary of a rod linkage connected to the actuator, which is of the jack screw type. The position control means consists of a proportional analog position sensor, which is arranged close to at least one edge of the conveyor belt, in proximity to the superposed horizontal rollers of the sealing head, where this sensor is connected to a calculation means that delivers a correction signal to a control servo-variator of the actuator of the means for positioning the frame or moving body holder. The sensor forming the position control means is an optic sensor, a pneumatic sensor, a Foucauld current sensor, or a probing sensor.
The device according to the last document makes it possible to ensure a good control of the drift of a conveyor belt, by continuous correction, regardless of what the advance speed of the belt is, and thus a correct positioning of said belt. However, its implementation still requires relatively complex means.